#ifndef COMMON_TIMESTAMP_H_
#define COMMON_TIMESTAMP_H_
#include <ctime>
#include <cstdint>

namespace fermat {

class Timespan;

/*!
* A Timestamp stores a monotonic* time value
* with (theoretical) microseconds resolution.
* Timestamps can be compared with each other
* and simple arithmetic is supported.
*
* [*] Note that Timestamp values are only monotonic as
* long as the systems's clock is monotonic as well
* (and not, e.g. set back due to time synchronization
* or other reasons).
*
* Timestamps are UTC (Coordinated Universal Time)
* based and thus independent of the timezone
* in effect on the system.
*
* The internal reference time is the Unix epoch, 
* midnight, January 1, 1970.
	*/
class Timestamp {
public:
	/*!
	* Monotonic UTC time value in microsecond resolution,
	* with base time midnight, January 1, 1970.
	*/
	typedef int64_t TimeVal; 

	/*!
	* Monotonic UTC time value in 100 nanosecond resolution,
	* with base time midnight, October 15, 1582.
	*/
	typedef int64_t UtcTimeVal; 

	/*!
	* Difference between two TimeVal values in microseconds.
	*/	
	typedef int64_t TimeDiff;

	static const TimeVal kTIMEVAL_MIN; //!< Minimum timestamp value.
	static const TimeVal kTIMEVAL_MAX; //!< Maximum timestamp value.

	/*!
	* Creates a timestamp with the current time.
	*/
	Timestamp();
	
	/*!
	* Creates a timestamp from the given time value
	* (microseconds since midnight, January 1, 1970).
	*/
	Timestamp(TimeVal tv);

	/*!
	* Copy constructor, copy a Timestamp from another one.
	*/
	Timestamp(const Timestamp& other);
		
	/*!
	* Destroys the timestamp
	*/
	~Timestamp();

	/*!
	* assign operators
	*/	
	Timestamp& operator = (const Timestamp& other);
	Timestamp& operator = (TimeVal tv);
	
	/*!
	* Swaps the Timestamp with another one.
	*/
	void swap(Timestamp& timestamp);
	
	/*!
	*Updates the Timestamp with the current time.
	*/
	void update();
	
	bool operator == (const Timestamp& ts) const;
	bool operator != (const Timestamp& ts) const;
	bool operator >  (const Timestamp& ts) const;
	bool operator >= (const Timestamp& ts) const;
	bool operator <  (const Timestamp& ts) const;
	bool operator <= (const Timestamp& ts) const;
	
	Timestamp  operator +  (TimeDiff d) const;
	Timestamp  operator +  (const Timespan& span) const;
	Timestamp  operator -  (TimeDiff d) const;
	Timestamp  operator -  (const Timespan& span) const;
	TimeDiff   operator -  (const Timestamp& ts) const;
	Timestamp& operator += (TimeDiff d);
	Timestamp& operator += (const Timespan& span);
	Timestamp& operator -= (TimeDiff d);
	Timestamp& operator -= (const Timespan& span);
	
	
	/*!
	*@return the timestamp expressed in time_t.
	* time_t base time is midnight, January 1, 1970.
	* Resolution is one second.
	*/
	std::time_t epochTime() const;
	
	/*!
	*@return the timestamp expressed in UTC-based
	* time. UTC base time is midnight, October 15, 1582.
	* Resolution is 100 nanoseconds.
	*/	
	UtcTimeVal utcTime() const;

	/*!
	*@return  the timestamp expressed in microseconds
	* since the Unix epoch, midnight, January 1, 1970.
	*/	
	TimeVal epochMicroseconds() const;
	
	/*!
	*@return   the time elapsed since the time denoted by
	* the timestamp. Equivalent to Timestamp() - *this.
	*/	
	TimeDiff elapsed() const;
	
	/*!
	*@return  true iff the given interval has passed
	* since the time denoted by the timestamp.
	*/	
	bool isElapsed(TimeDiff interval) const;
	
	/*!
	*@return  the raw time value.
	* Same as epochMicroseconds().
	*/
	TimeVal raw() const;
	
	/*!
	*@return  Creates a timestamp from a std::time_t.
	*/
	static Timestamp fromEpochTime(std::time_t t);
	
	/*!
	*@return  Creates a timestamp from a UTC time value
	* (100 nanosecond intervals since midnight,
	* October 15, 1582).
	*/
	static Timestamp fromUtcTime(UtcTimeVal val);
	
	/*!
	*@return  the resolution in units per second.
	* Since the timestamp has microsecond resolution,
	* the returned value is always 1000000.
	*/
	static TimeDiff resolution();

private:
	TimeVal _ts;
};


inline bool Timestamp::operator == (const Timestamp& ts) const
{
	return _ts == ts._ts;
}


inline bool Timestamp::operator != (const Timestamp& ts) const
{
	return _ts != ts._ts;
}


inline bool Timestamp::operator >  (const Timestamp& ts) const
{
	return _ts > ts._ts;
}


inline bool Timestamp::operator >= (const Timestamp& ts) const
{
	return _ts >= ts._ts;
}


inline bool Timestamp::operator <  (const Timestamp& ts) const
{
	return _ts < ts._ts;
}


inline bool Timestamp::operator <= (const Timestamp& ts) const
{
	return _ts <= ts._ts;
}


inline Timestamp Timestamp::operator + (Timestamp::TimeDiff d) const
{
	return Timestamp(_ts + d);
}


inline Timestamp Timestamp::operator - (Timestamp::TimeDiff d) const
{
	return Timestamp(_ts - d);
}


inline Timestamp::TimeDiff Timestamp::operator - (const Timestamp& ts) const
{
	return _ts - ts._ts;
}


inline Timestamp& Timestamp::operator += (Timestamp::TimeDiff d)
{
	_ts += d;
	return *this;
}


inline Timestamp& Timestamp::operator -= (Timestamp::TimeDiff d)
{
	_ts -= d;
	return *this;
}


inline std::time_t Timestamp::epochTime() const
{
	return std::time_t(_ts/resolution());
}


inline Timestamp::UtcTimeVal Timestamp::utcTime() const
{
	return _ts*10 + (TimeDiff(0x01b21dd2) << 32) + 0x13814000;
}


inline Timestamp::TimeVal Timestamp::epochMicroseconds() const
{
	return _ts;
}


inline Timestamp::TimeDiff Timestamp::elapsed() const
{
	Timestamp now;
	return now - *this;
}


inline bool Timestamp::isElapsed(Timestamp::TimeDiff interval) const
{
	Timestamp now;
	Timestamp::TimeDiff diff = now - *this;
	return diff >= interval;
}


inline Timestamp::TimeDiff Timestamp::resolution()
{
	return 1000000;
}


inline void swap(Timestamp& s1, Timestamp& s2)
{
	s1.swap(s2);
}


inline Timestamp::TimeVal Timestamp::raw() const
{
	return _ts;
}


} 


#endif

